1. Field of the Invention
The present invention relates to a bearing unit which rotatably supports a rotation shaft or rotatably supports a rotation member on the shaft and a motor and an electronic apparatus each having the bearing unit.
This application claims priority of Japanese Patent Application No. 2004-030987, filed on Feb. 6, 2004, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
Conventionally, a structure shown in FIG. 1 is known as a bearing unit which rotatably supports a rotation shaft.
The bearing unit 100 shown in FIG. 1 rotatably supports a rotation shaft 101, and has a radial bearing 104 which supports the rotation shaft 101 in the circumferential rotation about the rotation shaft 101, a spacing member 120 on which a thrust bearing 110 supporting an end of the rotation shaft 101 in the thrust direction is formed, and a housing 105 which contains the radial bearing 104 and the spacing member 120.
In this bearing unit 100, the radial bearing 104 constructs a dynamic fluid bearing together with a lubricant oil which is a viscous fluid filled in the housing 105. A dynamic pressure generation groove 111 is formed in the inner circumferential surface in which the rotation shaft 101 is inserted to generate a dynamic pressure.
A spacing member 120 provided at one end side of the rotation shaft 101 in the thrust direction is formed to surround a lower part of the rotation shaft 101, i.e., an end thereof at the closed side, as shown in FIG. 1. For example, the spacing member 120 is made of synthetic resins. Inside the spacing member 120, a hydraulic oil is filled around a bearing support part 102 of the rotation shaft 101.
A thrust bearing 110 supporting rotatably the bearing support part 102 provided at one end side of the rotation shaft 101 that is supported by the radial bearing 104 in the thrust direction is formed integrally at a center part in the inner surface side of the bottom of the spacing member 120. The thrust bearing 110 shares the spacing member 120 which is integrally made of resins. The thrust bearing 110 is formed as a pivot bearing which supports, at one point, the bearing support part 102 of the rotation shaft 101 formed in like an arc or tapered shape.
As shown in FIG. 1, the housing 105 which contains the radial bearing 104 and the spacing member 120 has such a shape that contains and surrounds the radial bearing 104 formed in a cylindrical shape. The housing 105 is thus a member formed by integrally molding synthetic resins.
The housing 105 is constituted by a cylindrical housing body 106, a bottom shielding part 107 which constructs an end part formed integrally with the housing body 106 so as to close an end side of the housing body 106, and an upper shielding part 108 formed integrally with the housing body 106 which constructs the other end side of the housing body 106. A bearing insertion hole 109 in which the rotation shaft 101 supported rotatably by the radial bearing 104 contained in the housing 106 is inserted is provided at a center part of the upper shielding part 108.
In the housing 105 thus constructed, synthetic resin material is subjected to outsert molding so as to surround the cylindrical radial bearing 104 and spacing member 120. Thus, the radial bearing 104 is integrally formed and provided in the inner peripheral side of the housing body 106.
The rotation shaft 101 is supported, on one end side thereof, by the bearing support part 102 and the thrust bearing 110. The outer circumferential surface of a shaft body 103 is supported by the radial bearing 104. The side of the attachment part of the rotation shaft 101, which is provided on the other end side, is protruded from the shaft insertion hole 109 provided in the upper shielding part 108 of the housing body 106. The rotation shaft 101 is thus supported on the housing 105.
The rotation shaft 101 also is provided with a groove part 116 for stopping the shaft provided between the bearing support part 102 and the shaft body 103. The spacing member 120 is provided with a circular washer 115 as a shaft stopper member, so as to correspond to the groove part 116 as a shaft stopper. The washer 115 prevents the rotation shaft 101 from being pulled out of the housing 105.
As shown in FIGS. 2 to 4, the washer 115 is attached to the groove part 116 of the rotation shaft 101. That is, as shown in FIG. 2, the rotation shaft 101 is inserted in the housing 105 having the radial bearing 104, the spacing member 120, and washer 115. Next, as shown in FIG. 3, the washer 115 provided in the spacing member is pressed against the bearing support part 102 of the rotation shaft 101 and is deformed in the thrust direction. The bearing support part 112 is thus inserted. Further, as shown in FIG. 4, the rotation shaft 101 is installed in the housing, at such a position in which the bearing support part 112 penetrates the washer 115 and the shaft stopper groove part 116 is situated inside the washer 115. At this time, the washer 115 is not deformed any more but has a normal shape and is set on the shaft stopper groove part 116 of the rotation shaft 101. The washer 115 attached to the rotation shaft 101 prevents the rotation shaft 101 from being pulled out of the housing 105.
Meanwhile, the shaft insertion hole 109 is formed to have an inner diameter slightly greater than the outer shape of the shaft body 103, such that the rotation axis 101 inserted in the shaft insertion hole 109 might not slide on the inner circumferential surface of the shaft insertion hole 109. At this time, the shaft insertion hole 109 is formed so as to have a gap 112 of a distance x5, enough to prevent a hydraulic oil 113 filled between the circumferential surface and the outer circumferential surface of the shaft body from leaking out of the housing 105.
A tapered part 114 is provided on the outer circumferential surface opposed to the inner circumferential surface of the shaft insertion hole 109 of the rotation shaft 101. This tapered part 114 is inclined to enhance the gap 112 formed between the outer circumferential surface of the rotation shaft 101 and the inner circumferential surface of the shaft insertion hole 109, toward the outside of the housing 105. This tapered part 114 creates a pressure gradient with respect to the gap 112 formed between the outer circumferential surface of the rotation shaft 101 and the inner circumferential surface of the shaft insertion hole 109, and generates a force which draws the hydraulic oil 113 filled in the housing 105 toward the inside of the housing 105. When the rotation shaft 101 is rotated, the hydraulic oil 113 is drawn into the inside of the housing 105, so that the hydraulic oil 113 steadily enters into the dynamic pressure generation groove 111 of the radial bearing 104 composed of a dynamic pressure fluid bearing, thereby generating a dynamic pressure. The rotation shaft 101 is thus supported stably, and the hydraulic oil 113 filled in the housing 105 can be prevented from leaking.
In the bearing unit 100 constructed as shown in FIG. 1, the rotation shaft 101 is exposed only at one end in the side of the shaft insertion hole 109. The other parts of the rotation shaft 101 than the shaft insertion hole 109 are covered seamlessly by a housing member. Therefore, the bearing unit 100 can prevent the hydraulic oil 113 from leaking to the outside of the housing 105. In addition, since the part communicating with the outside is only the gap of the shaft insertion hole 109, the hydraulic oil can be prevented from scattering due to impact. Further, due to the washer 115, the bearing unit 100 can prevent the rotation shaft 101 from being pulled out of the housing 105.
However, in the bearing unit 100 described above, the washer 115 needs to be warped when the rotation shaft 101 is inserted in the housing and the washer 115 is attached to the rotation shaft 101. A gap x3 between the radial bearing 104 and the washer 115 as well as a gap x4 between the washer 115 and the rotation shaft 101 needs to be provided.
Therefore, the bearing unit 100 has a structure in which the rotation shaft 101 is movable vertically over a range equivalent to the gap x3 and the gap x4. In the bearing unit 100, when the rotation shaft is lifted up from the housing, by a distance equivalent to the gaps x3 and x4, the liquid surface of the hydraulic oil 113 lowers down by the distance by which the rotation shaft moves from the liquid surface of the hydraulic oil. At this time, air enters into the bearing unit from the shaft insertion hole 109, driving away the hydraulic oil 113 in the gap between the radial bearing 104 and the shaft body 103 of the rotation shaft 101. This may involve a hindrance to the rotation performance of the bearing unit. Alternatively, air which has once entered may swell due to influences from the temperature and the air pressure, and the hydraulic oil may leak to the outside of the unit.
To prevent this problem, the dimension x6 of the upper end surface of the housing 105 may be elongated from the upper end surface of the radial bearing 104 to ensure a sufficient amount of hydraulic oil. Then, the height dimension of the bearing unit has to be enlarged. Another measure is conceivable in which the gap x5 between the shaft insertion hole 109 and the outer shape of the rotation shaft 101 may be widened to ensure the amount of hydraulic oil. However, the widening of the gap x5 may result in leakage of hydraulic oil when the unit is used, placed laterally, or has a vibrating impact.